If I understand correctly, you have a UI rule that is triggered by a change in the Remarks field. If a known location is typed in the Remarks field, it displays the address and contact name of the location.
I assume that by "location" you mean "organization" (because in OVSD "locations" do not have addresses or contact names).
What can go wrong ? 1) Your rule has been changed, or is blocked. 2) Your data is changed, so you are no longer finding the related information. 3) The information being typed is not exactly right (perhaps there are spaces or lower case letters instead of capitals). 4) There is a bug in OVSD resulting in intermittent execution of UI rules (I believe that such bugs have been documented and corrected by certain Service Packs).
Unless you provide some more information, it is difficult to diagnose.
This prilimnary check i have done i found the rule is working not blocked and location is typed properly without any space or Caps while typing. Looks this is all fine but as u said i doubt some bug is attacked our database.
Pls find the below attachment in history created by name shows Suma where in this lady had joined recently to our org and her id was created couple of days before but donno why the created by name is showing her's it was actually created by other login id.